The invention relates to an arrangement in a soda recovery boiler.
The invention further relates to a method in a soda recovery boiler.
In a pulp production process, black liquor is burnt in a soda recovery boiler. The tasks of a soda recovery boiler include recovery of chemicals and recovery of thermal energy generated in the burning process.
The soda recovery boiler comprises a furnace fed with black liquor and air required for combustion. An upper part of the boiler is provided with superheaters, and a flue gas duct after the superheater area. In the flue gas duct reside a boiler bank and economizers. The thermal energy generated in the burning process is used for producing superheated high-pressure steam to be used, inter alia, in the production of electricity.
When the temperature of the superheated steam is to be raised, some of the superheaters may be arranged in a second pass, i.e. in a first duct part of the flue gas duct after the boiler. Consequently, the temperature of the surfaces of the second pass may rise too much.